Earthquake Dragon

{14}{G}Creature — Elemental Dragon10/10

This spell costs {X} less to cast, where X is the total mana value of Dragons you control.

Flying, trample

{2}{G}, Sacrifice a land: Return this card from your graveyard to your hand.

Flying. This creature can't be blocked except by creatures with flying or reach. · CR 702.9

Trample. Excess combat damage beyond what's lethal to blockers can be assigned to the player or planeswalker it's attacking. · CR 702.19

Earthquake Dragon's last ability can be activated only if it is in your graveyard. (2022-06-10)
The total cost to cast Earthquake Dragon is locked in before you pay that cost. For example, if you control three Dragons, each with mana value 4, including one you can sacrifice to add {C}, the total cost of Earthquake Dragon is {2}{G}. Then you can sacrifice the Dragon as you activate mana abilities just before paying the cost. (2022-06-10)
If a permanent has {X} in its mana cost, X is 0 when calculating its mana value. (2022-06-10)
Once a player has announced that they are casting Earthquake Dragon, no player may take actions to try and change the number of Dragons its controller controls before that spell's cost is locked in. (2022-06-10)
If the total mana value of Dragons you control is 14 or greater, Earthquake Dragon costs {G} to cast. (2022-06-10)